Loudspeaker system



Jan. 13, 1942.- M. APPENZELLER LOUDSPEAKER SYSTEM Filed Nov. 9, 1940 LL L H m mm. H TZ N NNgR E .0 VW T A Y B ate-rated Jan. 13,

Telefunken Gesellschaft fiir Drahtlose 'ljelegraphic in. b. IL, Berlin, Germany, a corporation of Germany Application November 9, 1940, SerialINo. 364,957

6 Claims.

Establishments of morethan average size, restaurants, assembly halls, etc., are often equipped with loudspeakers, with one or more small-sized units being installedin the various rooms. Such loudspeaker installation serves to distribute news of all kinds, for instance, for reception of broadcast programs, reproduction and repetition of general instructions, and the like. Loudspeaker installations of this nature covering the entire plant or establishment offer a number of :advantages. For instance, works addresses and'similar activities are feasible immediately practically without any preparation, with only "a minimum loss of working time.

Over and above :these purposes, loudspeaker installations as here concerned, where introduced and adopted on a more general and comprehensive scale, very soon demonstrated their" utility for special problems of an organizational and technical nature. stallations were used for the transmission of air caution and alarm signals (preliminary alert, warning and restoration of normal condition or all clear signal), of instructions and orders of the air warden, fire alarm signals, stop-work sgnals and search for lost persons.

Such uses to which loudspeaker installations were put made it necessary to make conditions so that from the central oilice' certain signals should be transmissible to the loudspeaker at all times, even when the latter is disconnected from the transmission line itself. This according to the invention is insured by connecting with the various loudspeaker units two transformers having their primary and secondary windings arranged in series, the circuit organization being so chosen that, according to the nature of the signals to be transmitted only one transformer is operative at a given time. This condition, for instance, is insured by uniting the junction point of the two primary windings with one of the leads brought from the amplifier,-while the other two terminals of the two primary windings are connected with a change-over switch designed.

to short-circuit during normal operations the alarm operation the primary winding of the other transformer. I

The appended drawing illustrates an exemplified embodiment of the object of the invention. Associated with loudspeaker L are two transformers TI and T2, the primaries and secondaries of which are connected in series, The primary windings are indicated by PI and P2, the

For instance, loudspeaker in-.

Germany August 15, .1939

the circuitfpt the primary winding PI is an L,-type resistance pad R to-control the loudspeaker volume. An amplifier mounted at the central point or station is indicated by A. The dot anddash line X serves to indicate the separation between the central station at the left and remote loudspeakers L at the right. The junction point A of the primary windings'Pl and P2 is united with one of the leads, I, brought l from the amplifier A. The other terminal of the mary winding PI is brought to the lead 2, an d that of the primary, winding P2 of the second transformer to the lead 3; Leads 2 and 3 are connected with a change-over switch 5.; In the position indicated by the solid lines, which:

' corresponds to normal" operation conditions, transformer TI is connected with the output of the amplifier A. The primary winding P2 of the second transformer is short-circuited. If, then,

the switch S is thrown over to occupy the posi tion indicatedby the dash-lines and this occurs whenever orders, say, air protection signals or instructions of the works management are to be transmitted, the primary winding Pfof the transformer TI is short-circuited and the potentials prevailing in the output circuit of the amplifier are impressed upon the primary winding P2 of the second transformer. As can be seen from the circuit diagram, it is immaterial which 3o position the regulating resistance pad R occupies.

i the transmission of one kind of message, the

third wire and one of the first'two wires constituting a second transmission line and being reserved for the transmission of another kind of message, a loudspeaker at a remote point, cou-- pling means between each transmission line and primary winding of one transformer, and during the loudspeaker, a signal- .source at a central point, and control means at the central. point for selectively connecting the signal source to said first or second transmission line depending upon the kind of message it is desired to be transmitted to the remote point.

2. A signalling system comprising a three-wire transmission line, two of said wires constituting a first transmission line and being reserved for secondary windings by SI and S2, Included in 5b the {transmission of one kind of message, the

coupling means between each transmission line 5 and the loudspeaker, an audio amplifier at a central point provided with a pair or output terminals one of which is connected to the wire common to both transmission lines, and switch means at the central point for selectively con- 10 necting the other amplifier output terminal to the remaining wire of one or the other trans- =mission line depending upon the kind of message it is desired to be transmitted to the remote point line, one of said wires being directly connected to one o! the amplifier output terminals, switch means for selectively connecting the other output terminal to the two remaining wires of the transmission line, a pair of transformers the primaries and secondaries of which are connected respectively in series, a connection from the common terminal of the primaries to the first mentioned transmission line wire, connections from the remaining terminals of the primaries to respectively the remaining transmission line wires. and a loudspeaker connected across the transformer secondaries.

5. A loudspeaker system comprising an audio and-simultaneously short-circuitingthe coupling l5' ampliil'er at is central point, a plurality of loudmeans connected to the inoperative transmission line. i

'sp akerapne flqrffiii'ofe bi which are located at one or'more'remiite 'points, a transmission line 3. A loudspeaker system comprising an audio" interconnected'firetween said amplifier and loudampliflerat-a central point, at' least-one loudspeakers,-means fat the remote point individual speaker M718. re'm'ote'point, 'a"three-wi reftrans" '20 to eachloudspeiiker for connecting and disconmission line associated with said audio amplifier a pair of transformers the primaries and secondaries 01' which are connected respectively in" series, connections from each wire oi'th'e transtransformer' primaries, means for connecting the loudspeaker across the transformen'secondaries', Q

amplifier ata central point, at least one loudspeaker at a remote point, a transmission line and switch means at the central point 'so' 'constructed and arrangedthat-in either-oi its two positions one oF'the' 'transIormer primaries is 0 selectively short-circuitediwhile the use: pri mary is operative to transmit tnesignei from the amplifier to the loudspeaker.

4. A signalling system comprising an audio nectingr fthe loudspeaker .irom the transmission liiie;-"andfmeansfat the central point for oper- '1' ""a'tin'gsaid loudspeakers even though the discon- W necting means'has been operated whereby the mission line to respectively the terminals 01 the 25 loudspeakers are at all times under complete COIitI'OI of the amplifier at the central point.

6; A loudspeaker system comprising an audio interconnectedbetween' said amplifier and loudspeaker, a pair of transformers each having a primary and 'a' secondary Ior coupling the loudspeaker to the transmission line, and switch means at the central point selectively short-ciramplifler at a central point provided with a pair 35 cuiting one of said transformer primaries.

or output terminals, a three-wire transmission ax APPENZEILER. 

